[rules-users] populating global variable in Condition Section?

[Shah, Malay]

Yeah. It is much faster. Thanks Laun and Greg! We will see if the performance improvement is sufficient by removing exists. I always thought "not" was a logical boolean operator here, but it looks like an implicit existence check operator. 

Regards,
Malay Shah

-----Original Message-----
From: rules-users-bounces at lists.jboss.org [mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Greg Barton
Sent: Friday, August 21, 2009 11:45 PM
To: Rules Users List
Subject: Re: [rules-users] populating global variable in Condition Section?

Of course, I had to test that assertion. :)

$ java -Xmx128M -server -jar target/DroolsExistence-1.0.jar not.drl 50000 25000 2395ms $ java -Xmx1024M -server -jar target/DroolsExistence-1.0.jar not_exists.drl 50000 25000 121378ms

You ain't kiddin'! 50x slower requiring 9x the memory.

--- On Fri, 8/21/09, Wolfgang Laun <wolfgang.laun at gmail.com> wrote:

> From: Wolfgang Laun <wolfgang.laun at gmail.com>
> Subject: Re: [rules-users] populating global variable in Condition Section?
> To: "Rules Users List" <rules-users at lists.jboss.org>
> Date: Friday, August 21, 2009, 4:54 PM  <quote> It is rather common 
> for people to
>             write something like "(not (exists (A)))," but this is 
> just a
>             very inefficient way to write (not (A)).
> </quote>
> 
> Kudos to Ernest Friedman-Hill to put this sentence into the Jess 
> documentation.
> 
> Maybe I should quote hiom in the Drools Expert doc ;-)
> 
> 
> -W
> 
> 
> On Fri, Aug 21, 2009 at 11:11 PM,
> Shah, Malay <Malay.Shah at morganstanley.com>
> wrote:
> 
> May be I have not put the question right. We have a drool rule that is 
> running extremely slow for large sets of data.
> The rule is something like:
> 
> 
> 
> For every object A, perform action if there does not exist an object B 
> such that A.id = B.id.
> 
> And the corresponding drool rule is as follows:
> 
> 
> 
> when
> 
>     A()
> 
>     not(exists B(A.id = id))
> 
> then
> 
>     action......
> 
> 
> 
> The performance is bad because of not exists clause here.
> We have got OOM exceptions with relatively large amounts of data for 
> this rule. To improve performance, we basically hacked the rule/code 
> into something like this:
> 
> 
> 
> 
> Create a global variable x that is a HashSet of all ids of object A, 
> and the drool rule now is:
> 
> 
> 
>  global java.util.HashSet x;
> 
> when
> 
>         B()
> 
>         eval
> 
>         (
> 
>                 ! (x.contains(b.id) )
> 
>         )
> 
> then
> 
>         action.....
> 
> 
> 
> This obviously is performing much better with hashes involved. But, I 
> don't like the fact that we have to write the logic of this rule at 
> two places. I would rather create this variable x (don't care whether 
> it is global or temporarily bound) in the rule itself and use it in 
> the condition to help performance and have all logic for the rule at 
> one place.
> 
> 
> 
> 
> Is there a way to generate this hashset x in the condition part of the 
> rule itself? Yes, I understand that I am trying to mix up the 
> procedural part of code with drool code. But, I was just wondering if 
> this is possible to keep the java code clean and have the intelligence 
> of information that the rule needs to be evaluated in the rule itself.
> 
> 
> 
> 
> Hope this clears some doubts.
> 
> 
> 
> Thanks
> 
> 
> 
> Malay Shah
> 
> 
> 
> -----Original Message-----
> 
> From: rules-users-bounces at lists.jboss.org
> [mailto:rules-users-bounces at lists.jboss.org]
> On Behalf Of Greg Barton
> 
> 
> Sent: Friday, August 21, 2009 4:44 PM
> 
> To: Rules Users List
> 
> Subject: Re: [rules-users] populating global variable in Condition 
> Section?
> 
> 
> 
> This is a galactically bad idea.  Using a global in this way is 
> inherently unsafe as there's no guarantee that ebtween the time you 
> set the var and when it's used later in the condition that the value 
> is the same.  What is your reason for wanting to use a global in this 
> way?  You should use a temporary bound variable instead.
> 
> 
> 
> 
> --- On Fri, 8/21/09, Shah, Malay <Malay.Shah at morganstanley.com>
> wrote:
> 
> 
> 
> > From: Shah, Malay <Malay.Shah at morganstanley.com>
> 
> > Subject: [rules-users] populating global variable in
> Condition Section?
> 
> > To: rules-users at lists.jboss.org
> 
> > Date: Friday, August 21, 2009, 3:19 PM
> 
> >
> 
> >
> 
> >
> 
> >
> 
> >
> 
> >
> 
> > Hi,
> 
> >
> 
> > Is it possible
> 
> > to populate a global variable in
> 
> > the condition section of the
> 
> > drool rule, and use it later in the condition itself?
> 
> > I currently have a
> 
> > global HashSet variable that I construct before firing
> the rule, but I
> 
> > would like this code of constructing this global
> variable to be with
> 
> > the drool rule itself. Any help on this would be much
> appreciated.
> 
> >
> 
> > Thanks
> 
> >
> 
> > Malay
> 
> >
> 
> >
> 
> >
> 
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